The Arch Example

abstract: We show you, how you can use blender to create sculpted prims with high precision. This tutorial will show you some techniques for building high precision sculpted prims. We used blender 2.46 for all demonstration sequences. As an example we have choosen the construction of a sculpted window frame for a casino window front.

When you want to create an arch, always use standard prims! Just make a simple prim cube , then use path-cut, and for the hollow shape select: circle. And finally set the value of hollow to about 90. Or just take a cylinder, again use path-cut, and hollow, and you are done. This is quick and easy going. You definitely do not need sculpted prims to make arches …

But sometimes the standard is not sufficient enough. For instance look here: When you go close to the object, then you see that the surface is not completly smooth. This is, because prim cylinders use poly-gons with 24 edges. And since we use only the half of a cylinder in this example here, we end up with only 12 edges positioned along the bended line.

Now suppose you want to make a castle entrance door, or you want to build a window frame which contains a bow. In both cases the results are not perfectly continuous. So: When detail matters, standard prims are not enough.

ok! the title of this tutorial already implies what comes next: Of course we are going to look at precision sculpties. We can count on 2 main points here.

first, sculpty cylinders use 32 edges. While prim cylinders use only 24 edges.

we have almost full control over the vertex positions of the sculpties.

We will use these possibilities, and eventually, we will end up with much better results compared to standard prims. Please keep in mind, that in most cases standard prims are sufficient for your building, so please use them frequently. Only in special cases you will need to use precision sculpties to get better results.

So let us begin with an \stress=yes example. For the machinima “we only live twice”, we need to make the window front of a casino building. We started with standard prims and created the following result.

That already looks pretty good, but this was \stress=yes not enough for us. We want to make a very detailed and nice looking building. So we used blender \pause=0 , to develop a technique for precise sculpting.

Ok, let us begin with Step 1:

Start with a cube with a good vertex distribution. Of course the level of detail (LOD) is important for us, because the casino front shall look similar from all camera positions. And finally we want to have as many vertices as possible along the line of curvature. I have already prepared an initial cube with 13 vertices along the x-axis, 5 vertices along y , and 33 vertices along z. Creating such a cube from scratch should be no big problem. You can see how to do that in our tutorial about LOD.

At the moment this object uses the dimensions of a unit cube. All sides have a length of 1 unit. We also have to take into account, that OpenSim and many other compatible online worlds support only 256 distinct steps along each axis. The only possible values are mapped to a range from -128 up to +127. If we do not care about that, we possibly will end up in a disaster. Please keep in mind, that this is only valid, when you need precision sculpties. If you are making organic shapes, then the roughness of the grid might not be of concern for you.

Step 2: Prepare the grid

We choose the following settings to allow what i call “snap to Sculptie grid”. This will help me to ensure, that the relative positions of all vertices are preserved during the step of sculptie baking. For this purpose we place all mesh points of the sculptie on a grid, that exactly corresponds to the sculptie resolution.

We will work in object mode now.

I open view -> view properties

and set the grid values as follows:

For the grid spacing i use 0.01 units.

For the number of divisions i choose 1.

I open object -> transform ->properties

and set all 3 dimensions to 2.55.

Then i check that the object location is zero. If you examine the object in detail now, you will see, that at this moment all vertices are slightly shifted away from the grid. We will come back to this in a later step.

Step 3: Prepare the cube

We will work in top view now. First we rotate the cube along the y-axis by 90 degrees .

Then, in object mode, we scale down the y-axis to span over a distance of exactly 8 grid-units. We can enter the data directly into the transform properties window. At the end we have a straight stick. Of course you can scale the y-axis to other settings depending on your needs.

We will transform the stick into a half circle now. it is important to bend along the x-axis. The reason for doing it this way is to achieve the best resolution along the curvature. And the best resolution is currently available along the x-axis. There we count 33 vertices. This is about three times more compared to the solution, which is based on a half prim cylinder.

Step 4: Bending the cube.

Now we will transform the stick into a bow with an outer radius of 1.275.
So the bow will span over the full available space in the x-direction, which is 2.5 5 .
But first i will shift the object down by 4 grid points in the y-direction, so that the upper side is aligned exactly to the median point.

Now we mark the anticipated position of the center of the bow. Therefore we place the 3D cursor exactly on the y-axis (x=0) and choose -1.275 for y.

Now we do the final step. We will create the bow by using the warp tool:

In edit mode press

SHIFT -> W

and enter a value of “180” on the key-board. This means, warp around the 3D cursor, limit the bending to 180 degrees. Hence the stick gets transformed into a half circle with a radius of 1.275

Get back to object mode and ensure , that the dimensions of “x” and “z” are still 2.55.
The “y” dimension should be 1.275 at this moment.

We will do a couple of preparations now, which we need later for keeping the bow as precise as possible. So let us advance to

Step 5: Prepare for manual optimizations.

Go to object mode, create an additional circle and place it exactly on the outer side of the bow. This circle will help us later for adjustments . Be sure, that you are in object mode, then enter

add -> mesh -> circle.

Set the radius to 1, and the number of vertices to 128, then scale it up. In our case i simply create it at the center of the bow, and scale it up to 1.275 .

Now enter edit mode and create a secnd circle in the same way but scale it up until it is positioned on top of the inner line. In this case we again can create it at the center of the bow but now we scale it to 1.195, so the distance to the outer circle is exactly 8 units.

Finally we are going to remove the lower half of the helper circles. Now the helper object is ready for usage.

– Back in Object mode, keep the helper circles selected, open the view properties and place the 3D cursor at the median-point of the bow.

– Then click

Object -> transform -> Center cursor.

– Now the median points of both objects are equal, so the next step is very easy:

– Open the transform properties, and set a value of 2.55 for all dimensions.

– Do the same for the Bow object.

– Finally adjust the object positions slightly, so that the lower-left corner is positioned exactly on the grid.

And finally we are ready for

Step 6: do the fine adjustments.

– choose only the bow, and go to edit mode for the last fine tuning.

– Let us first check, what happens, when we apply snap to grid now. this looks good, but not too precise.

And this is of course because our grid is too rough. So we have to align the vertices by hand. Let us go to the top of the construction first, and work our way down to the bottom. Take the vertices one by one, and reposition them along the curvature of the helper circles, while carefully choosing only crosspoints between the grid and the circles. So you ensure, that all important vertices of your object keep exactly adjusted.

Now proceed further down. Try to keep the curvature as smooth as possible. You will have to experiment a bit until you find good vertex positions.

The right part of the bow is now corrected. Now we have to take care about the left part.
But instead of repeating the tedious process of adjusting the vertices, we will use a mirror now:

– First, i will remove the left half of the vertices. Ok, this does not work, when multires is active.
Hence, i need to apply multires now. Then removing the vertices works as expected.

– Now i create a mirror-modifier, so that all modifications, which i applied on the right side of the bow, will also be mirrored to the left side.

– Take care to also mirror the “V”-texture-coordinate.
– If You don’t do this, your UV-map contains only half of the needed data.

Now, After all these steps are performed, finally bake the sculptie, import it to OpenSim (or your preferred compatible world) and watch the results.

6 Enlightened Replies

I think this tutorial is lacking somewhere. I follow it all the way through and then get to the mirror modifier, do it all just like it says and i still end up with a half a bow that’s really horrible in world…oO

So you can not get the mirror modifier to create the missing half of the bow, or does the bake step not work ? Can you explain in a little ore detail what exactly is going wrong ? maybe show some images ?

hmmmmm… not sure what is going on here… but got all the way up to the step where you apply the mirror modifier and it will not apply it. Tells me that I cant do that in the edit mode. I am not sure if it is the version that I am working with, 2.48a, or what, but its frustrating to get this far through the tutorial and then have Blender not perform as shown. Otherwise, great tutorial, and the problem I am having, could very well be me missing something. 🙂

Well, I am not sure about the cube. I make the cube like the 8 step quickie in LOD, but how can you alter the number of vertices along each axis when the cube is ready for the burn. You can’t delete of add ?